1. Field of Invention
The present invention relates to an electrophoretic display which utilizes the movement of electrophoretic particles in a medium due to application of an electric field, and a method of producing the same.
2. Description of Related Art
Japanese Unexamined Patent Publication (Kokai) No. 64-86116 and Japanese Unexamined Patent Publication (Kokai) No. 10-149118 disclose inventions of electrophoretic displays using microcapsules.
FIG. 7 is an elementary sectional view for illustrating an example of a conventional electrophoretic display using microcapsules.
In the electrophoretic display 1, a transparent substrate 3 provided with transparent electrodes 51 to 53 and a transparent back substrate 2 having a transparent electrode 4 are arranged at a predetermined distance d so that the transparent electrode 4 and the transparent electrodes 51 to 53 face each other.
The transparent substrate 3 and the back substrate 2 are formed by using an insulating synthetic resin such as PET (polyethylene terephthalate).
The transparent electrode 4 and the transparent electrodes 51 to 53 are formed by, for example, transparent electrode films (ITO (indium oxide) films).
A large number of microcapsules 6 are arranged between the transparent substrate 3 and the back substrate 2.
The microcapsules 6 are sealed with (comprise) a dispersion comprised of electrophoretic particles 7 dispersed in a dispersion medium 11 (dispersion system) in advance by the microcapsulation technique. In natural state, these shapes are spherical.
The electrophoretic particles 7 are comprised of charge particles, for example, white pigment.
The dispersion medium 11 is comprised of a colored dispersion medium, for example, colored black.
Hereinafter, the liquid mixture between the electrophoretic particles 7 and dispersion medium 11 sealed in the microcapsules 6 will also be referred to as the electrophoretic display dispersion.
Between the transparent substrate 3 and the back substrate 2, the large number of microcapsules 6 and a binder 8 for fixing the large number of microcapsules 6 are inserted.
The binder 8 is transparent and has good bondability with the transparent electrodes 4 and 51 to 53.
In this configuration, for example, when making the transparent electrode 4 the ground potential and applying a negative voltage to the transparent electrodes 51 and 53, electrophoretic particles 7, that is, the charged particles, inside the microcapsules 6 between the transparent electrode 4 and the transparent electrodes 51 and 53 move toward the transparent electrode 4. As a result, the microcapsules 6 between the transparent electrode 4 and the transparent electrodes 51 and 53 exhibit a black color with respect to the direction of the transparent substrate 3.
Further, if making the transparent electrode 4 the ground potential and applying a positive voltage to the transparent electrode 52, electrophoretic particles 7, that is, the charged particles inside the microcapsules 6 between the transparent electrode 4 and the transparent electrode 52 move toward the transparent electrode 52. As a result, the microcapsules 6 between the transparent electrode 4 and the transparent electrode 52 exhibit a white color with respect to the direction of the transparent substrate 3.
An electrophoretic display having spherical microcapsules seal with an electrophoretic display dispersion, suffers from the following disadvantages (1) and (2).
(1) The portions between the spherical microcapsules, that is, the binder portions, do not contain electrophoretic particles, so the contrast may be liable to be lowered.
(2) The electric field intensity acting on the electrophoretic display dispersion in the spherical microcapsules positioned between the electrodes becomes nonuniform, so localization of the electrophoretic particles may be liable to be caused.
Japanese Unexamined Patent Publication (Kokai) No. 10-149118 discloses making the dielectric constant the same between the electrophoretic display dispersion and binder to make the electric field intensity uniform, but if this is done, limits arise in the selection of the materials used for the electrophoretic display dispersion and binder.